Add overflow:auto scrollbars to child flex basis.

Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2366 matching lines @@
 
 LayoutUnit LayoutBox::computeContentAndScrollbarLogicalHeightUsing(SizeType heightType, const Length& height, LayoutUnit intrinsicContentHeight) const
 {
     if (height.isAuto())
         return heightType == MinSize ? 0 : -1;
     // FIXME(cbiesinger): The css-sizing spec is considering changing what min-content/max-content should resolve to.
     // If that happens, this code will have to change.
     if (height.isIntrinsic()) {
         if (intrinsicContentHeight == -1)
             return -1; // Intrinsic height isn't available.
-        return computeIntrinsicLogicalContentHeightUsing(height, intrinsicContentHeight, borderAndPaddingLogicalHeight());
+        return computeIntrinsicLogicalContentHeightUsing(height, intrinsicContentHeight, borderAndPaddingLogicalHeight()) + scrollbarLogicalHeight();
     }
     if (height.isFixed())
         return height.value();
     if (height.hasPercent())
         return computePercentageLogicalHeight(height);
     return -1;
 }
 
 bool LayoutBox::skipContainingBlockForPercentHeightCalculation(const LayoutBox* containingBlock) const
 {
@@ skipping 2336 matching lines @@
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender(*this, style()->effectiveZoom()) && borderImage->isLoaded();
 }
 
 ShapeOutsideInfo* LayoutBox::shapeOutsideInfo() const
 {
     return ShapeOutsideInfo::isEnabledFor(*this) ? ShapeOutsideInfo::info(*this) : nullptr;
 }
 
 } // namespace blink